Cell Division

Question 1

Proteins Responsible for driving the cell cycle

Answer 1

Cohesins.

Condensins

Centromeric heterochromatin

Spindle architecture

Question 2

Cohesins

Answer 2

Cohesins are a protein complexes that hold replicated chromosomes (chromatids) together until they can be accurately separated by the spindle apparatus in M- phase. A cohesin complex is made up of Smc (Structural maintenance of chromosomes) protein subunits and accessory (Scc) proteins. It is thought that a cohesin complex binds chromatids together by encircling their DNA strands like in the cartoon to the right; many complexes are found along the length of the chromatids.

Question 3

Condensins

Answer 3

Condensins. The onset of M-phase is marked by
chromosome condensation, which allows
chromosomes to be separated in a more
manageable fashion. Also, decatenation of any
entangled DNA strands remaining from the
process of replication occurs, with the end result being the production of two compact sister chromatids that can be readily separated in anaphase without the risk of chromatin breakage. Condensins are protein complexes that carry out these functions. Like cohesins, condensins are made up of subunits of Smc proteins and other accessory (CAP) proteins. The exact mechanisms by which condensins coil and compact chromatin are not yet understood, but it may form a ring-like structure that encircles loops of
DNA.

Question 4

Centromeric heterochromatin

Answer 4

Centromeric heterochromatin. Centromeres of chromosomes contain a special histone H3 variant called CENP-A. Chromatin in this region is especially tightly compacted, and forms a scaffolding for the assembly of protein complexes that form the kinetochore. The purpose of the kinetochore is to interact with microtubules of the spindle apparatus so that daughter chromatids can be separated.

Question 5

What are the two primary ways Cdk activity is regulated?

Answer 5

full activation of Cdk requires cyclin

binding and a specific pattern of Cdk phosphorylation

Question 5

What are the two primary ways Cdk activity is regulated?

Answer 5

full activation of Cdk requires cyclin

binding and a specific pattern of Cdk phosphorylation

Question 6

How is S-phase triggered?

Answer 6

Activation of G1-Cdk results in the production of G1/S and S cyclins (E and A, respectively), and subsequent activation of G1/S-Cdk, which drives the cell through the restriction point (start), and commits the cell to complete a round of cell division. G1/S-Cdk activates S-
Cdk, which in turn triggers DNA synthesis.